Method of purifying aluminous materials



Dec. 27, 1938. M, NORDBERG 2,141,444

METHOD OF PURIFYING ALUMINOUS MATERIALS Filed March 16, 1937 "III..." I.I. mxvgey amounts. sx; vans;-

F .2 e3 l9 u I IN V EN TOR. M9,? rm 1: Womaasxa- BY: yv a-Q ATTORNEYS.

Patented Dec. 27, 1938 UNITED STATES METHOD OF PURIFYING ALUMINOUSMATERIALS Martin E. Nordberg,

Corning Glass Wor ration of New York Application March 16,

1 Claim.

This invention relates to methods of purifying ceramic materials, andmore particularly high alumina materials such as kaolin, kyanite,bauxite, diaspore and the like.

Anv important object of theinvention is to remove iron and iron bearingimpurities from the materials and thus provide a cheap source of purealumina, for use in making glass, enamels, porcelain and other ceramicproducts.

Another object is to whiten clays and other aluminous materials so thatthey will be more suitable for use as fillers for paper, textiles, etc.

A further object is to prevent any-substantial loss of alumina duringthe treatment for removal of iron.

This invention'consists in converting the iron impurity to chloride format elevated temperatures and volatilizing the iron chloride andseparating it from the material under conditions which 2 will permit theuse of a minimum quantity of chlorine or its compounds to remove themaximum amount of iron but at the same time to cause substantially noloss of alumina.

Since the iron impurity in clay is present largely as iron oxide, thetotaliron content will be considered for convenience as if it wereferric oxide and it is to be understood that other compounds of ironwhich may be present will also react and be converted to chloride duringthe proc- 30 ess to be described.

Ferric oxide at elevated temperatures reacts with chlorine to formferric chloride in accordance with the following equation:

35 The reaction is reversible. At equilibrium below 1100 C. the ratio ofthe partial pressure of chlorine to the partial pressure of ferricchloride is high and hence it is necessary to use a large excess ofchlorine. Such a procedure requires-too great an expenditure of chlorineto be economically feasible and even though means were to be employed torecover the uncombined chlorine the attendant expense would increase 45the cost of the purified material unduly. With high aluminous materialscontaining less than F8203, it has been found that practically six timesas much chlorine is required as would be expected from equilibrium datafor the above re- 50 action with pure ferric oxide. This indicates thatin the case of clay the ferric oxide is in a state of solid solutionwith the alumina, wherefore the activity of the iron oxide will dependupon its concentration and relatively more chlorine will be required fordilute solutions.

The use of a large excess of chlorine may be avoided by reducing thepartial pressure of the oxygen resulting from Equation 1 to a minimum.Since the partial pressure of the oxygen liberated 5 is very low, apowerful reducing agent is required.

Corning, N. Y.., assignor to Corning, N. Y., a corpo- 1937, Serial No.131,265

O+2C=2CO (2) The combined Equations 1 and 2 then becomeFe2Os+3C+3C12=2FeC13+3CO (3) Ordinarily, in this case the loss ofalumina is very pronounced because the formation of aluminum chloride isin like manner also facilitated by the presence of carbon.

I have discovered, however, that at temperatures of 900 C. to 1150 0.,when the amount of carbon is kept low and the chlorine is passed throughor over the material at a very slow rate, substantially all of the ironis converted to ferric chloride and is volatilized out of the materialwithout appreciable loss of alumina. For example, I have removed about83% of the iron from a calcined clay, which initially contained about..4% ferric oxide and to which 1% of lamp black had been added, bypassing 3 cc. of chlorine per minute per grams of clay through thematerial at a temperature of 1075 C. for 30 minutes. The above quantityof chlorine is lessthan one-seventh the amount that would berequired ifno 30 carbon were present. I have also found that a temperature above900 C. is necessary to effect a satisfactory separation of iron fromaluminous materials, as is clearly indicated by the following tablewhich shows the results obtained at various temperatures and withvarious rates of flow of chlorine for 10 gram samples of a calcinedkaolin containing .42% F820: to which 1% of lamp black was added andthoroughly mixed therewith. This amount of carbon is substantially tentimes the amount that would theoretically be required and represents themaximum proportion of carbon which I have found it desirable to use.

Chlorine Lossin Resid- Ratio of Ratio of 21 C. weigh ual A140 weight Clin per Fez0; lost used to cent in per- Fez 0; F810:

cent removed removed cc. per min.

it will be noted that at tem- C'. very little iron is removed,

From the above data peratures below 900 although the amount of chlorineused in proportion to the iron removed is very high and the loss ofalumina as compared to loss of iron is V correspondingly low.

' and the fact that most of the relatively great. On the other hand, attemperatures of 900 C. and above the iron content is materially andsatisfactorily decreased with a relatively small expenditure of chlorineand the loss of alumina as compared to the'loss of iron is The effect oflow rates of flow is particularly noticeable in regard to expenditure ofchlorine and loss. of respect to iron removed.

The apparatus required is very simple and may consist of any suitablereceptacle, which is capable of being heated and of being closed toexclude air, which will not into which the material to be treatedtogether with the chlorine may be introduced as will later be described.I

It is believed that the efficiency of my process may be explained atleast in part as follows: Some of the alumina and iron are converted tochlorides in accordance with the reactions shown in Equations (4) and(5), the-amount of alumi num chloride formed being in very great excesson account of the high concentration of alumina iron is enclosed withinthe grains. ,With too rapid a flow of chlorine the aluminum chloridewould be swept out of the zone of reaction and the available carbonwould thus be used up with consequent loss of alumina and only a smallremoval of iron for the amount of chlorine used. However, by passing thechlorine at a sufficiently slow rate, the aluminum chloride is notquickly swept out but remains in the reaction zone. The aluminumchloride diffuses into the grains and since aluminum oxide is morestable than iron oxide or has a higher heat of formation, it reacts withthe unconverted iron oxide in the material as follows:

The idifiusion maybe facilitated by a change in the physical structureof the grains which is due to a recrystallization that occurs above 870C. If the amount of carbon present is calculated, from the known amountof iron present, to be slightly in excess of that necessary to satisfythe requirement of Equation (4) substantially all of the ferric oxidewill be converted to ferric chloride by the aluminum chloride accordingto Equation (5) and volatilized and since the amount of carbon was smallthere will be substantially no loss of alumina.

Instead of introducing the chlorine continuously at a slow. rate thetotal equivalent amount thereof may be introduced and withdrawnintermittently, under pressure if necessary, the requisite being that itshouldbe kept in contact with the material for the time required toobtain the same result and such a modification of the process is withinthe scope of this invention.

Another embodiment of my invention consists in using in lieu of thechlorine gas of Equation (1) the vapor of a chloride of an element whoseoxide is more stable than ferric oxide, such as silicon tetrachloride,aluminum chloride and titanium tetrachloride. The reaction which occurswith aluminum chloride is indicated above in Equation (5). The otherreactions are:

3SiCl4+2Fe2Os=3SiO2+4FeCla (6) 3TiC14+2Fe2Oa=3TiOz+4FeCl3 ('7) Incarrying out the process according to the reactions set forth inEquations 5, 6 and '7, the aluminous material is heated to a temperatureis excluded from the apparatus.

alumina with be attacked by chlorine and oi 900-1l50 C. and the vapor ofthe chloride is passed through and over the material while air It isimportant that oxidizing agents or free oxygen, such as air, be absentbecause this would cause oxidation of the chlorinating agents andreoxidation of the ferric chloride in a manner analogous to the reversalof Equation 1, a condition which is here sought to be avoided. Theamount of chloride vapor used and the rate at which it is introduced isgoverned only by economic considerations. In other words, the chloridevapor should be introduced at such a rate and for such a time as willinsure maximum reaction with the ferric oxide without undue waste of thechlorinating agent. The proper rate and time may readily be determinedby trial.

'- be understood, reference is had to the accompanying drawing whichillustrates the simplest form of apparatus adaptable for carrying out myinvention, it being understood that the process as claimed may becarried out in various types of apparatus without departing from thespirit and scope of the invention.

Fig. 1 is a view partly in section of anapparatus for purifyingaluminous material with chlorine gas, and Y Fig. 2 is a view partly insection of an apparatus for purifying aluminous material with chloridevapors.

In the drawing in which corresponding parts are designated bycorresponding marks of reference, a tube in composed of non-ferrousmaterial which is resistant to chlorine or chloride vapors, such assilica, and provided with a spiral-' ly wound electrical heating elementH and an insulating jacket 12 is mounted on a supporting table 13 Oneend of the tube I is provided with a delivery tube M which may be eitherof silica or of glass. The other end of the tube It! is provided with atube of silica or of glass which serves to introduce chlorinating vaporsinto the tube l0. Each end of the tube i0 is closed by plugs iii ofrefractory material to exclude air, the tubes l4 and I5 passing snuglytherethrough. The tube [0 contains a quantity of material [1 which is tobe treated.

I In Fig. 1 a chlorine tank l8 having a pressureregulating value I9 isconnected meter 20 to the tube l5.

In Fig. 2 a flask 2| containing a volatile chlo: ride to be vaporized issupported upon an electric hot plate 22 and is provided with anelectrically heated delivery tube 23 which is connected to the tube l1.

In practicing my invention a quantity oi aluminous material to betreated is mixed with 1 to 10 times the. amount of carbon theoreticallynecessary to satisfy Equation (3), depending on the iron content of thematerial. The mixture is placed in the tube In which is connected with asource of chlorine and is sealed against the en-' trance of air as shownin Fig. 1. The tube and its contents are then heated by means of theheating element II to a 11 50 C. and chlorine is introduced through thetube IS, the rate of flow being regulated by the valve l9 and the flowmeter 20 to about 2l0 cc. per minute. The ferric chloride which isformed by the reaction is vaporized and issues from the delivery tubel4.

Instead of mixingthe carbon with the total through a flow may beadvantageous to mix temperature of 900 only a small portion of thematerial and to place the carbonaceous mixture in the tube I0 adjacentthe non-carbonaceous material but in such position that the incomingchlorine will pass first through the carbonaceous mixture. By this meansthe carbon, being in very large excess in the carbonaceous mixture willbe used up in forming therefrom aluminum chloride in accordance with.the reaction represented in Equation (4). The aluminum chloride vaporthus formed will permeate the adjacent non-carbonaceous material andwill react therewith to form ferric chloride and to revert to aluminumoxide in accordance with Equation (5), the ferric chloride beingvaporized and eliminated from the material. This modification of myprocess has the advantage that the aluminum chloride vapor formed mustpass through all of the material with consequent better eiiiciency.

In the modification of my process which is il- Iustrated in Fig.

2, a quantity of a chloride, such 3 as silicon tetrachloride, aluminumchloride or titanium tetrachloride, is heated in the flask 2! by the hotplate 22 and the vapor is passed through the heated tube 23 and throughthe material I! which in this instance contains no carbon.

I claim:

The method of removing iron from high alumina materials, which includesmixing with a small quantity of the material from one to ten times theamount of carbon necessary to satisfy the equationF6203+3C+3C12=2FeCl3+3CO, based on the initial iron content of a totalbatch of the material to be treated, placing the carbonaceous mixtureadjacent the non-carbonaceous batch, heating the whole to a temperatureof 900-1150 C. while excluding air and introducing chlorine gas so as topass first through the carbonaceous mixture.

MARTIN E. NORDBERG.

